Power consumption
We measured the power consumption of our entire test systems, except for the monitor, at the wall outlet using a Watts Up PRO watt meter. The test rigs were all equipped with OCZ PowerStream 520W power supply units. The idle results were measured at the Windows desktop, and we used SMPOV and the 64-bit version of the POV-Ray renderer to load up the CPUs. In all cases, we asked SMPOV to use the same number of threads as there were CPU front ends in Task Manager—so four for the Pentium XE 840, two for the Athlon 64 X2, and so on.

The graphs below have results for "power management" and "no power management." That deserves some explanation. By "power management," we mean SpeedStep or Cool'n'Quiet. In the case of the Pentium XE 840 CPU, the C1E halt state is always active, even in the "no power management" tests. The Extreme Edition 955 and the P4 Extreme Edition 3.73GHz don't support the C1E halt state or SpeedStep.

The FX-60 and Extreme Edition 955 consume exactly the same amount of power at idle—until AMD's Cool'n'Quiet kicks in and the FX-60's power use drops by 45 watts. It's unfortunate than Intel chose not to include power management in the Extreme Edition 955.

The move to 65nm serves the Extreme Edition 955 well. Despite having more L2 cache, more transistors, and a higher clock frequency, it uses less power under load than the Extreme Edition 840. Sadly for Intel, the process shrink isn't sufficient to close the power consumption gap with AMD's amazing dual-core Athlons, which barely require more power than their single-core counterparts.